INSECT DEPREDATIONS IN NORTH AMERICAN FORESTS. 69 



dead bark on the trunks would contribute to the spreading of crown 

 fires and thus the bark on the entire infested trunks would be suiR- 

 ciently scorched to kill the insects. Therefore, complete fire control 

 may easily contribute to more extended depredations by insects on the 

 living timber, thus increasing, rather than diminishing, the need for 

 insect control. However, the setting of fires or permitting them to 

 burn for the purpose of combating insects should never be under- 

 taken or permitted. 



Durability of insect-7iiUcd timher. — Some of the matured larch 

 trees which evidently died as a result of defoliation by the larch 

 worm between 1881 and 1885, and which had escaped subsequent 

 depredations by fire and wood-boring insects, were found by the 

 writer in 1908 to be standing and sound enough to be utilized for 

 railroad ties and many other purposes. Under similar conditions the 

 heartwood of red spruce and white pine in the East, of Engelmann 

 spruce in the Rocky INIountains, and of Douglas fir in the Northwest 

 coast region have been found by the writer to be sound enough for 

 -profitable utilization for pulp wood, lumber, fuel, and other pur- 

 ,. poses from twenty to thirty years after it had been killed by insects 

 or fire. Thus it is shown that timber killed by insects and fire would 

 be available for utilization for many years were it not for injuries 

 through the secondary attacks of wood-boring insects and the de- 

 struction of insect-killed timber by forest fires. 



INTERRELATION OF FOREST INSECTS AND FOREST FUNGI. 



Decay following injury by insects. — It is well Imown that the 

 burrows in the bark and wood of living and dead trees and in 

 the crude and finished products often contribute to the entrance of 

 bark and wood decaying fungi. Deterioration and decay are thus 

 far more rapid than would otherwise be possible. It is also known 

 that trees injured and dying from primary attack by parasitic fungi 

 are attractive to certain insects which breed in the bark and wood 

 of sickly and dying trees, and that certain other complicated troubles 

 affecting forest trees are the result of an intimate interrelation and 

 interdependence of insects and fungi. There can be no doubt, how- 

 ever, that certain species and groups of both insects and fungi are 

 independently capable of attacking and killing perfectly vigorous 

 and healthy trees. 



SUMMARY AND ESTIMATES RELATING TO CHARACTER AND EXTENT OP 



INSECT DAMAGE. 



The killing of trees by insects ; the damage by them to the wood 

 of living, dying, and dead timber; the destruction of insect-killed 

 timber by subsequent forest fires; the damage to fire-killed timber 

 by insects; and the damage from decay resulting from insect injuries 

 to the wood, have all been more or less continuous for centuries and 

 are still going on in the forest and woodland areas of this country. 



